The invention herein pertains to conditioning air for a building and particularly pertains to removing moisture from the outside air to improve the efficiency of refrigeration systems therein.
Fresh outside air brought into a building through the HVAC system contains moisture which impacts the efficiency and expense of operating internal refrigeration systems (refrigeration furniture such as food display cases and the like). While such efficiency loss and operational expense may be nominal in homes or small offices, in larger commercial establishments moisture can severely impact refrigeration furniture and greatly increase the operational cost in a relatively short period of time. This is particularly true in businesses such as shops and stores which require relatively high tonnage HVAC systems such as in a typical grocery store of 38,000 square feet, having a 50-60 tonnage HVAC system operating under standard conditions.
An HVAC system must provide a comfortable environment for the workers and shoppers and ideally would prevent problems from occurring with refrigeration furniture such as medium temperature (0xc2x0-32xc2x0 F.) open display cases containing meat or produce and low temperature (0xc2x0 F. or below) closed cases which accommodate frozen foods. As all refrigeration furniture utilizes evaporator coils, such coils can xe2x80x9cfreezexe2x80x9d or form ice on the outside surfaces due to the humidity present. When a coil is xe2x80x9cfrozenxe2x80x9d, the refrigeration circuit is ineffective and may result in the goods thawing or spoiling. Even in instances where the goods are not severely damaged, the operation of the refrigeration furniture is lessened, causing high power consumption and increased expense as it operates.
Thus, in view of the problems and expenses which can occur with improper moisture levels in the conditioned air space in buildings such as grocery stores, the present invention was conceived and one of its objectives is to provide an apparatus and method for conditioning entering outside air of the HVAC system to allow optimum efficiency of the internal refrigeration system;
It is another objective of the present invention to provide a method for staging the compressors of the HVAC systems according to the wet bulb temperature of the outside air as it enters the HVAC system;
It is still another objective of the present invention to measure the sensible temperature of the outside air with an electronic temperature measuring sensor and to measure the relative humidity by a conventional electronic sensor before said air enters the conditioned air space;
It is yet another objective of the present invention to calculate the wet bulb temperature from the sensible air temperature and the relative humidity, utilizing a microprocessor;
It is a further objective of the present invention to stage the HVAC compressors according to the calculations of the wet bulb temperature and to compare the wet bulb temperature to preselected wet bulb set points of the compressor(s) capacity (such as by MBH and/or horsepower) whereby the moisture in the conditioned air is reduced so that the refrigeration furniture within the building operates efficiently (such as with their evaporator coils free of frost and ice);
It is yet a further objective of the present invention to provide an HVAC system having a pair of unequal capacity compressors which operate within four stages for maximum efficiency and the least amount of HVAC horsepower utilized.
Various other objectives and advantages of the present invention will become apparent to those skilled in the art as a more detailed description is set forth below.
The aforesaid objectives are achieved by providing an HVAC system for a grocery store or other building to monitor and closely control the moisture in the conditioned air space. Treating the outside air in the method disclosed provides optimum efficiency of the internal refrigeration systems such as for example, refrigeration furniture cases as follows:
Step 1: The sensible temperature of the outside air is measured by a conventional electronic sensor before it enters the conditioned air space;
Step 2: The relative humidity of the outside air is measured by a conventional electronic sensor before it enters the conditioned air space;
Step 3: The wet bulb temperature is calculated from the sensible air temperature and the relative humidity measurement by a microprocessor which converges the wet bulb temperature by calculating a known polynomial; and
Step 4: Unequal size (horsepower) compressors are staged according to the calculations of the microprocessor to remove moisture from the outside air before it enters the conditioned air space.
The two measured points (sensible air temperature and relative humidity) are used to calculate the wet bulb temperature of the incoming air. The wet bulb temperature is compared to preselected set points of the HVAC compressors which in turn remove the moisture from the air passing through the HVAC cooling coils. The set points of the compressors are compared to the wet bulb temperature calculated by a microprocessor using the measured sensible temperature and relative humidity so that the evaporator coils of the HVAC condensing unit remove maximum moisture from the outside air, thus preventing the cooling coils of the refrigerant furniture from freezing.
The HVAC unequal size compressors are staged as follows:
Stage 1) both compressors off;
Stage 2) the smaller compressor on and the larger off;
Stage 3) the smaller compressor off and the larger on; and
Stage 4) both compressors on.
This staging or compressor control maximizes the moisture removal from the outside air before it is brought into the conditioned air space, allowing peak efficiency of the refrigeration furniture cases with the least amount of HVAC (compression) horsepower expended for a minimum energy consumption. For example, in stage 2 the smaller compressor which may be a 7xc2xd horsepower compressor would operate while the larger, 15 horsepower compressor does not. Any wet bulb temperature below 57.2xc2x0 F. would freeze the evaporator coils of the HVAC systems so any wet bulb temperature above that set point (57.2xc2x0 F.) would activate stage 2, creating a minimum suction temperature of 32xc2x0 F. If the wet bulb temperature increases, the microprocessor will cycle the compressors on and off into the four stages as required. A time delay circuitry (set at 30 minutes) is employed whereby the staging will not be subjected to radical staging changes.